This invention relates, in general, to semiconductor devices, including, but not limited to, a gallium arsenide device having a short gate length and a method of fabricating it.
An important feature of gallium arsenide devices, such as MESFETs (Metal Semiconductor Field Effect Transistors) or HEMTs (High Electron Mobility Transistors), is its gate length. The length of the gate is directly proportional to the frequency response of these gallium arsenide devices. Devices having a shorter gate length enable higher frequency responses to be achieved. Devices fabricated by standard processing typically have a 20 GHz capability. It would be desirable to fabricate a MESFET having a 100 GHz capability. However, in the past there has been a limit as to how short gate lengths can be fabricated using standard processing techniques, due to the processing constraints of present standard photolithographic means. A way of achieving shorter gate lengths is by using electron beam technology rather than standard photolithographic means. However, electron beam processing is not very manufacturable and is very expensive to use at this time. It would also be desirable to fabricate devices having a short gate length without the use of electron beam technology using a self-aligned gate process. A self-aligned gate process provides for better reproducability and reduces some parasitic capacitances in the device.